A modified collagen gel enhances healing outcome in a preclinical swine model of excisional wounds

Development of a Static Avascular and Dynamic Vascular Human Skin Equivalent Employing Collagen/Keratin Hydrogels

One of the primary complications in generating physiologically representative skin tissue is the inability to integrate vasculature into the system, which has been shown to promote the proliferation of basal keratinocytes and consequent keratinocyte differentiation, and is necessary for mimicking representative barrier function in the skin and physiological transport properties. We created a 3D vascularized human skin equivalent (VHSE) with a dermal and epidermal layer, and compared keratinocyte differentiation (immunomarker staining), epidermal thickness (H&E staining), and barrier function (transepithelial electrical resistance (TEER) and dextran permeability) to a static, organotypic avascular HSE (AHSE). The VHSE had a significantly thicker epidermal layer and increased resistance, both an indication of increased barrier function, compared to the AHSE. The inclusion of keratin in our collagen hydrogel extracellular matrix (ECM) increased keratinocyte differentiation and barrier function, indicated by greater resistance and decreased permeability. Surprisingly, however, endothelial cells grown in a collagen/keratin extracellular environment showed increased cell growth and decreased vascular permeability, indicating a more confluent and tighter vessel compared to those grown in a pure collagen environment. The development of a novel VHSE, which incorporated physiological vasculature and a unique collagen/keratin ECM, improved barrier function, vessel development, and skin structure compared to a static AHSE model.

Preparation and comparison of two medical dressings made from the collagens from fish and bovine

Collagen is used in medical dressings because of its high hydrophilicity, low immunogenicity, excellent biocompatibility, and degradability. These features can promote cell proliferation and platelet agglomeration. Herein, we studied the preparation of gel dressing by using silver carp skin collagen and bovine collagen as raw materials. Their properties and the application effects of collagen gel dressing were evaluated and compared. The centrifugal stability, rheology, and water-loss rate of silver carp skin collagen gel (SCG) and bovine tendon collagen gel (CTG) were determined. Results showed that the two gels were stable, and SCG had better rheology and ductility than CTG. However, the denaturation temperature and water-retention rate of SCG were slightly lower than those of CTG. Two collagen gels were used in the burn-repair experiment of KM mice. Results showed that the SCG and CTG were consistent with the wound-repair effect of commercially available products for shallow II-degree scald and deep II-degree scald. In the superficial shallow II scald experiment, SCG had a faster healing rate in the first 8 days and a shorter recovery time than CTG. In the deep II-degree scald experiment, the wound-healing rate of SCG on the 14th day reached 94.24%, which was 2 days faster than the recovery time of CTG. Moreover, the skin after wound healing was shallower than the scar produced after CTG treatment. Therefore, SCG had the potential to be used as the medical dressing.

Polymeric biomaterials-based tissue engineering for wound healing: a systemic review

Background

Biomaterials are vital products used in clinical sectors as alternatives to several biological macromolecules for tissue engineering techniques owing to their numerous beneficial properties, including wound healing. The healing pattern generally depends upon the type of wounds, and restoration of the skin on damaged areas is greatly dependent on the depth and severity of the injury. The rate of wound healing relies on the type of biomaterials being incorporated for the fabrication of skin substitutes and their stability in in vivo conditions. In this review, a systematic literature search was performed on several databases to identify the most frequently used biomaterials for the development of successful wound healing agents against skin damage, along with their mechanisms of action.

Method

The relevant research articles of the last 5 years were identified, analysed and reviewed in this paper. The meta-analysis was carried out using PRISMA and the search was conducted in major scientific databases. The research of the most recent 5 years, from 2017-2021 was taken into consideration. The collected research papers were inspected thoroughly for further analysis. Recent advances in the utilization of natural and synthetic biomaterials (alone/in combination) to speed up the regeneration rate of injured cells in skin wounds were summarised. Finally, 23 papers were critically reviewed and discussed.

Results

In total, 2022 scholarly articles were retrieved from databases utilizing the aforementioned input methods. After eliminating duplicates and articles published before 2017, ~520 articles remained that were relevant to the topic at hand (biomaterials for wound healing) and could be evaluated for quality. Following different procedures, 23 publications were selected as best fitting for data extraction. Preferred Reporting Items for Systematic Reviews and Meta-Analyses for this review illustrates the selection criteria, such as exclusion and inclusion parameters. The 23 recent publications pointed to the use of both natural and synthetic polymers in wound healing applications. Information related to wound type and the mechanism of action has also been reviewed carefully. The selected publication showed that composites of natural and synthetic polymers were used extensively for both surgical and burn wounds. Extensive research revealed the effects of polymer-based biomaterials in wound healing and their recent advancement.

Conclusions

The effects of biomaterials in wound healing are critically examined in this review. Different biomaterials have been tried to speed up the healing process, however, their success varies with the severity of the wound. However, some of the biomaterials raise questions when applied on a wide scale because of their scarcity, high transportation costs and processing challenges. Therefore, even if a biomaterial has good wound healing qualities, it may be technically unsuitable for use in actual medical scenarios. All of these restrictions have been examined closely in this review.

Rete ridges: Morphogenesis, function, regulation, and reconstruction

Rete ridges (RRs) are distinct undulating microstructures at the junction of the dermis and epidermis in the skin of humans and certain animals. This structure is essential for enhancing the mechanical characteristics of skin and preserving homeostasis. With the development of tissue engineering and regenerative medicine, artificial skin grafts have made great progress in the field of skin healing. However, the restoration of RRs has been often disregarded or absent in artificial skin grafts, which potentially compromise the efficacy of tissue repair and regeneration. Therefore, this review collates recent research advances in understanding the structural features, function, morphogenesis, influencing factors, and reconstruction strategies pertaining to RRs. In addition, the preparation methods and limitations of tissue-engineered skin with RRs are discussed. STATEMENT OF SIGNIFICANCE: The technology for the development of tissue-engineered skin (TES) is widely studied and reported; however, the preparation of TES containing rete ridges (RRs) is often ignored, with no literature reviews on the structural reconstruction of RRs. This review focuses on the progress pertaining to RRs and focuses on the reconstruction methods for RRs. In addition, it discusses the limitations of existing reconstruction methods. Therefore, this review could be a valuable reference for transferring TES with RR structure from the laboratory to clinical applications in skin repair.

Bioelectric fields coordinate wound contraction and re-epithelialization process to accelerate wound healing via promoting myofibroblast transformation

Electric fields (EFs) are thought to play a decisive role in wound healing. However, most studies focused on the effects of EF on single species of cells in vitro. Here, we aimed to investigate the coordination function of EFs on wound healing. Using a bamamini pig whole-layer wound model, we further evaluated the potential of EFs as a treatment modality by applying continuous and stable EF to the wound, and we found that EF promoted wound contraction and re-epithelialization in vivo, which accelerated wound healing. In vitro, we found that EFs significantly promoted the collective migration of HaCaT cells, guided HSF cells rearrangement, and promoted collagen secretion and myofibroblast transformation, and the electrotaxis of HaCaT cells was significantly enhanced on the collagen substrate and F-actin polarization at the leading edge of the cells was more pronounced. Overall, we determined that EF promotes wound contraction by promoting myofibrillar transformation, while accelerating the formation of collagen substrates, and the substrates could provide a good basis for electric field-guided re-epithelialization. EF may promote wound healing in multiple dimensions interaction and coordinate the whole process of wound healing. These findings provide support for the continued development of EF for wound treatment applications.

Gel dressing based on type I collagen modified with oligourethane and silica for skin wound healing

Cutaneous wound healing is a complex process that leads the skin reparation with the formation of scar tissue that typically lacks skin appendages. This fact drives us to find new strategies to improve regenerative healing of the skin. This study outlines, the contribution of colloidal silica particles and oligourethane crosslinking on the collagen material properties and the effect on skin wound healing in rats. We characterized the gel properties that are key forin-situgelation, which is accomplished by the latent reactivity of oligourethane bearing blocked isocyanate groups to crosslink collagen while entrapping silica particles. The swelling/degradation behavior and the elastic modulus of the composite gel were consistent with the modification of collagen type I with oligourethane and silica. On the other hand, these gels were characterized as scaffold for murine macrophages and human stem cells. The application of a composite gel dressing on cutaneous wounds showed a histological appearance of the recovered skin as intact skin; featured by the epidermis, hair follicles, sebaceous glands, subcutaneous adipose layer, and dermis. The results suggest that the collagen-based composite dressings are promising modulators in skin wound healing to achieve a regenerative skin closure with satisfactory functional and aesthetic scars.

Wound Healing Modulation through the Local Application of Powder Collagen-Derived Treatments in an Excisional Cutaneous Murine Model

Wound healing includes dynamic processes grouped into three overlapping phases: inflammatory, proliferative, and maturation/remodeling. Collagen is a critical component of a healing wound and, due to its properties, is of great interest in regenerative medicine. This preclinical study was designed to compare the effects of a new collagen-based hydrolysate powder on wound repair to a commercial non-hydrolysate product, in a murine model of cutaneous healing. Circular excisional defects were created on the dorsal skin of Wistar rats (n = 36). Three study groups were established according to the treatment administered. Animals were euthanized after 7 and 18 days. Morphometric and morphological studies were performed to evaluate the healing process. The new collagen treatment led to the smallest open wound area throughout most of the study. After seven days, wound morphometry, contraction, and epithelialization were similar in all groups. Treated animals showed reduced granulation tissue formation and fewer inflammatory cells, and induction of vasculature with respect to untreated animals. After 18 days, animals treated with the new collagen treatment showed accelerated wound closure, significantly increased epithelialization, and more organized repair tissue. Our findings suggest that the new collagen treatment, compared to the untreated control group, produces significantly faster wound closure and, at the same time, promotes a slight progression of the reparative process compared with the rest of the groups.

Large full-thickness wounded skin regeneration using 3D-printed elastic scaffold with minimal functional unit of skin

Traditional tissue engineering skin are composed of living cells and natural or synthetic scaffold. Besize the time delay and the risk of contamination involved with cell culture, the lack of autologous cell source and the persistence of allogeneic cells in heterologous grafts have limited its application. This study shows a novel tissue engineering functional skin by carrying minimal functional unit of skin (MFUS) in 3D-printed polylactide-co-caprolactone (PLCL) scaffold and collagen gel (PLCL + Col + MFUS). MFUS is full-layer micro skin harvested from rat autologous tail skin. 3D-printed PLCL elastic scaffold has the similar mechanical properties with rat skin which provides a suitable environment for MFUS growing and enhances the skin wound healing. Four large full-thickness skin defects with 30 mm diameter of each wound are created in rat dorsal skin, and treated either with tissue engineering functional skin (PLCL + Col + MFUS), or with 3D-printed PLCL scaffold and collagen gel (PLCL + Col), or with micro skin islands only (Micro skin), or without treatment (Normal healing). The wound treated with PLCL + Col + MFUS heales much faster than the other three groups as evidenced by the fibroblasts migration from fascia to the gap between the MFUS dermis layer, and functional skin with hair follicles and sebaceous gland has been regenerated. The PLCL + Col treated wound heals faster than normal healing wound, but no skin appendages formed in PLCL + Col-treated wound. The wound treated with micro skin islands heals slower than the wounds treated either with tissue engineering skin (PLCL + Col + MFUS) or with PLCL + Col gel. Our results provide a new strategy to use autologous MFUS instead "seed cells" as the bio-resource of engineering skin for large full-thickness skin wound healing.

Skin wound healing assessment via an optimized wound array model in miniature pigs

An appropriate animal wound model is urgently needed to assess wound dressings, cell therapies, and pharmaceutical agents. Minipig was selected owing to similarities with humans in body size, weight, and physiological status. Different wound sizes (0.07-100 cm²) were created at varying distances but fail to adequately distinguish the efficacy of various interventions. We aimed to resolve potential drawbacks by developing a systematic wound healing system. No significant variations in dorsal wound closure and contraction were observed within the thoracolumbar region between boundaries of both armpits and the paravertebral region above rib tips; therefore, Lanyu pigs appear suitable for constructing a reliable dorsal wound array. Blood flow signals interfered with inter-wound distances ˂ 4 cm; a distance > 4 cm is therefore recommended. Wound sizes ≥ 4 cm × 4 cm allowed optimal differentiation of interventions. Partial- (0.23 cm) and full-thickness (0.6 cm) wounds showed complete re-epithelialization on days 13 and 18 and strongest blood flow signals at days 4 and 11, respectively. Given histological and tensile strength assessments, tissue healing resembling normal skin was observed at least after 6 months. We established some golden standards for minimum wound size and distance between adjacent wounds for effectively differentiating interventions in considering 3R principles.

Collagen-Based Nanofibers for Skin Regeneration and Wound Dressing Applications

Skin regeneration after an injury is very vital, but this process can be impeded by several factors. Regenerative medicine is a developing biomedical field with the potential to decrease the need for an organ transplant. Wound management is challenging, particularly for chronic injuries, despite the availability of various types of wound dressing scaffolds in the market. Some of the wound dressings that are in clinical practice have various drawbacks such as poor antibacterial and antioxidant efficacy, poor mechanical properties, inability to absorb excess wound exudates, require frequent change of dressing and fails to offer a suitable moist environment to accelerate the wound healing process. Collagen is a biopolymer and a major constituent of the extracellular matrix (ECM), making it an interesting polymer for the development of wound dressings. Collagen-based nanofibers have demonstrated interesting properties that are advantageous both in the arena of skin regeneration and wound dressings, such as low antigenicity, good biocompatibility, hemostatic properties, capability to promote cellular proliferation and adhesion, and non-toxicity. Hence, this review will discuss the outcomes of collagen-based nanofibers reported from the series of preclinical trials of skin regeneration and wound healing.

Collagen in Wound Healing

Normal wound healing progresses through inflammatory, proliferative and remodeling phases in response to tissue injury. Collagen, a key component of the extracellular matrix, plays critical roles in the regulation of the phases of wound healing either in its native, fibrillar conformation or as soluble components in the wound milieu. Impairments in any of these phases stall the wound in a chronic, non-healing state that typically requires some form of intervention to guide the process back to completion. Key factors in the hostile environment of a chronic wound are persistent inflammation, increased destruction of ECM components caused by elevated metalloproteinases and other enzymes and improper activation of soluble mediators of the wound healing process. Collagen, being central in the regulation of several of these processes, has been utilized as an adjunct wound therapy to promote healing. In this work the significance of collagen in different biological processes relevant to wound healing are reviewed and a summary of the current literature on the use of collagen-based products in wound care is provided.

Evaluation of a cross-linked versus non-cross-linked collagen matrix in full-thickness skin defects

Autologous skin transplantation is the gold standard for treatment of full-thickness skin defects such as deep burn injuries, but has the disadvantages of limited donor sites and donor site morbidities. Alternative skin replacement products, such as xenografts and allografts, are not a permanent solution. Numerous manufactured skin substitutes already show promising approaches, but have limited efficacy. Therefore, wound dressings adaptable to the physiology of wound healing are still needed. In a randomized controlled in vivo study, a newly designed biocompatible collagen nonwoven matrix was compared to the Integra® bilayer dermal substitute and untreated controls in 48 full-thickness skin defects in a swine model. The take of all templates was complete, and all the tissue-engineered products accelerated dermal wound healing compared to the untreated controls, as identified by planimetric measurements. The higher collagen dose treatments and Integra®-covered wounds developed the thickest, cell-rich neoepidermal tissue in histological examination. The innovative biocompatible collagen matrix is flexibly applicable and modifiable, and offers potential as a carrier membrane for therapeutic supplemental products such as growth factors to further develop effective wound dressings.

Topical administration of mangiferin promotes healing of the wound of streptozotocin-nicotinamide-induced type-2 diabetic male rats

Purpose: This study identifies the potential use of mangiferin gel to promote wound healing in diabetes mellitus (DM).Materials and methods: Male rats were rendered diabetes mellitus via intraperitoneal injection of streptozotocin and nicotinamide. Following diabetes development, wound was created at the back of the neck. 1% and 2% mangiferin gel and 1% silver sulphurdiazine (SS) gel (positive control) were applied to the wound for twenty-one (21) days. Fasting blood glucose (FBG) levels were weekly monitored. At the end of the treatment, rats were sacrificed and wound was excised and subjected for histopathological and molecular biological analysis.Results: No changes to serum FBG levels was noted throughout the period of mangiferin treatment. Albeit, a significant decrease in the size of the wound with increased in the skin thickness of surrounding the wound were observed. Increased expression and distribution of EGF, FGF, TGF-β, VEGF, PI3K, MMP and Nrf2 and decreased expression and distribution of TNFα and NF-κB p65 were observed in diabetic wound treated with topical mangiferin.Conclusions: Mangiferin has potential to be used as an agent to promote wound healing in diabetic condition.

Development and characterization of an immunomodulatory and injectable system composed of collagen modified with trifunctional oligourethanes and silica

Immunomodulatory biomaterials have emerged as a promising approach to engineer wound healing. To achieve this task, the bioactivity of the biomaterials and an easy application are two key desirable characteristics. This work reports an injectable gel system containing immune cells primed for wound healing. By combining the self-assembly of type I collagen, cross-linked with trifunctional oligourethanes, and silica particle entrapment, the structured collagen network acts as a delivery vehicle for macrophages. This structured collagen network primes the macrophages for an anti-inflammatory response. Rheological measurements suggest that the mixture of liquid precursors can be safely stored at low temperatures and low pH (4 °C, pH 3) for at least one month. After pH neutralization and injection, gels with a storage modulus of 50-80 Pa are obtained in five minutes. Several immunocytochemistry and ELISA tests strongly suggest that mouse and human macrophages are stimulated by the material to up-regulate the production of anti-inflammatory cytokines, while down-regulating the production of pro-inflammatory cytokines. The injection of gel in an ex vivo inflammation model of intervertebral discs demonstrated that it is possible to transit from a pro-inflammatory to an anti-inflammatory microenvironment. Altogether, the results suggest that this gel can polarize the macrophage response and promote a surrounding anti-inflammatory microenvironment ready for injection for wound healing applications.

A Modified Collagen Dressing Induces Transition of Inflammatory to Reparative Phenotype of Wound Macrophages

Collagen containing wound-care dressings are extensively used. However, the mechanism of action of these dressings remain unclear. Earlier studies utilizing a modified collagen gel (MCG) dressing demonstrated improved vascularization of ischemic wounds and better healing outcomes. Wound macrophages are pivotal in facilitating wound angiogenesis and timely healing. The current study was designed to investigate the effect of MCG on wound macrophage phenotype and function. MCG augmented recruitment of macrophage at the wound-site, attenuated pro-inflammatory and promoted anti-inflammatory macrophage polarization. Additionally, MCG increased anti-inflammatory IL-10, IL-4 and pro-angiogenic VEGF production, indicating a direct role of MCG in resolving wound inflammation and improving angiogenesis. At the wound-site, impairment in clearance of apoptotic cell bioburden enables chronic inflammation. Engulfment of apoptotic cells by macrophages (efferocytosis) resolves inflammation via a miR-21-PDCD4-IL-10 pathway. MCG-treated wound macrophages exhibited a significantly bolstered efferocytosis index. Such favorable outcome significantly induced miR-21 expression. MCG-mediated IL-10 production was dampened under conditions of miR-21 knockdown pointing towards miR-21 as a causative factor. Pharmacological inhibition of JNK attenuated IL-10 production by MCG, implicating miR-21-JNK pathway in MCG-mediated IL-10 production by macrophages. This work provides direct evidence demonstrating that a collagen-based wound-care dressing may influence wound macrophage function and therefore modify wound inflammation outcomes.

Natural composite dressings based on collagen, gelatin and plant bioactive compounds for wound healing: A review

Skin wound dressings are commonly used to stimulate and enhance skin tissue repair. Even if wounds seem easy to repair for clinicians and to replicate in an in vitro set-up for scientists, chronic wounds remain currently an open challenge in skin tissue engineering for patients with complementary diseases. The seemingly simple process of skin healing hides a heterogenous sequence of events, specific timing, and high level of organization and coordination among the involved cell types. Taken together, all these aspects make wound healing a unique process, but we are not yet able to completely repair the chronic wounds or to reproduce them in vitro with high fidelity. This review highlights the main characteristics and properties of a natural polymer, which is widely used as biomaterial, namely collagen and of its denatured form, gelatin. Available wound dressings based on collagen/gelatin and proposed variants loaded with bioactive compounds derived from plants are presented. Applications of these composite biomaterials are discussed with emphasis on skin wound healing. A perspective on current issues is given in the light of future research. The emerging technologies support the development of innovative dressings based exclusively on natural constituents, either polymeric or bioactive compounds.

Electrospinning of in situ crosslinked recombinant human collagen peptide/chitosan nanofibers for wound healing

Electrospun collagen nanofibers are effective for wound healing; however, many problems, such as the tedious preparation process, weak strength and poor structure integration, limit further applications. In this study, recombinant human collagen (RHC) peptides and a simple one-step crosslinking strategy were used to prepare RHC/chitosan nanofibers. With the nonpathogenic, water-soluble RHC and a mild electrospinning solvent, in situ crosslinked nanofibers (S-CN) not only simplified the preparation procedure but also maintained a more integrated morphology. Compared with the immersed crosslinked nanofibers (I-CN), S-CN showed better performance in moisture retention, degradation and mechanical strength tests. In vitro cell proliferation, morphology and RT-PCR studies confirmed that fibroblasts presented better activities on nanofibers crosslinked in situ. Importantly, after treating with the nanofibers, rapid epidermidalization and angiogenesis were observed in an SD rat scalding model. All these data suggest that electrospun RHC/chitosan nanofibers crosslinked in situ are an ideal candidate that can be used for wound healing applications.

A porcine model for pathomorphological age assessment of surgically excised skin wounds

A porcine model of second intention wound healing was established and gross and histological changes needed for accurate assessing the age of wounds were determined. Twenty-five pigs were anesthetized before incision of four wounds on each. The wounds were left to heal from 1 h to 35 days when the pigs were euthanized. In 14 pigs, biopsies were sampled from two wounds between days 2 and 18. By histological evaluation the following characteristics were found useful for determining the age of wounds: neutrophil:macrophage ratio, angiogenesis, hyperplasia of fibroblasts, presence of hemosiderophages and granulation tissue. The latter was present from day 4 (n = 8 wounds, 100%), but by gross evaluation it was not recognized until day 5 (n = 4 wounds, 100%). From day 4 to 10, the thickness of granulation tissue increased by 1.2 ± 2.4 mm/day. The thickness of collagen fibers within granulation tissue increased throughout the study period, and complete epithelization was reached from day 18.

Fifty-Patient Study Evaluating the Efficacy of Modified Collagen With Glycerin in Periwound Skin Management

The management of chronic nonhealing ulcers pose a great challenge because they are associated with morbidity and increased costs. This report presents the observations of standard management along with application of modified collagen with glycerin (MCG) in the periwound area for management of nonhealing wounds. This observational report included 50 patients (33 male, 17 female) aged 24 to 94 years having nonhealing wounds. All wounds were treated using standard treatment protocols (TIME concept), whereas the periwound severity was assessed using the Harikrishna Periwound Skin Classification (HPSC). All patients received once-daily application of MCG lotion directly in the periwound areas and compression bandaging until there was complete wound healing. Patient compliance was ensured by regular follow-up and counseling. All diabetic patients were counseled to ensure glycemic control during the entire follow-up period. The criteria used for wound healing were based on clinical observation, and proper epithelialization of the wound was the end point. The median age of the wounds was 12.0 weeks (95% CI = 8.00 – 58.08). Majority of the non-healing wounds were diabetic foot ulcers with age of wound between 4 weeks to 15 years. The median time to complete wound healing was 12.71 (95% CI = 10.00-16.67) weeks. Standard treatment protocol of TIME principle with periwound area assessment based on HPSC 2015 and treatment accordingly with topical application of MCG along with additional measures has shown complete healing of nonhealing wounds. However, further large-scale comparative studies are needed to substantiate these effects on a larger population.

Novel mechanisms of Collagenase Santyl Ointment (CSO) in wound macrophage polarization and resolution of wound inflammation

Collagenases are useful in enzymatic wound debridement. Clostridial collagenase, marketed as Collagenase Santyl Ointment (CSO), is FDA approved for such use. Building on the scientific premise that collagenases as well as collagen degradation products may regulate immune cell function, we sought to investigate the potential role of CSO in wound inflammation. We tested the hypothesis that in addition to enacting debridement, CSO contributes to the resolution of persistent wound inflammation. Wound macrophages were isolated from PVA sponges loaded with CSO or petrolatum and implanted in mice. Significant increase in pro-reparative and decrease in pro-inflammatory polarization was noted in macrophages of acute as well as diabetic wounds. Wound macrophages from CSO-treated group displayed increased production of anti-inflammatory cytokines IL-10 and TGF-β, and decreased levels of pro-inflammatory cytokines TNF-α and IL-1β. The active ingredient of CSO, CS-API, induced the expression of mϕ^heal /M(IL-4) polarization markers ex vivo. CS-API treatment attenuated transactivation of NF-κB and significantly induced STAT6 phosphorylation. A significant role of a novel PGE2-EP4 pathway in CS-API induced STAT6 activation and the mϕ^heal /M(IL-4) polarization was identified. Taken together, findings of this work reposition CSO as a potential agent that may be effective in resolving wound inflammation, including diabetic wounds.

Significantly Accelerated Wound Healing of Full-Thickness Skin Using a Novel Composite Gel of Porcine Acellular Dermal Matrix and Human Peripheral Blood Cells

Here we report the fabrication of a novel composite gel from decellularized gal-gal-knockout porcine skin and human peripheral blood mononuclear cells (hPBMCs) for full-thickness skin wound healing. Decellularized skin extracellular matrix (ECM) powder was prepared via chemical treatment, freeze drying, and homogenization. The powder was mixed with culture medium containing hyaluronic acid to generate a pig skin gel (PSG). The effect of the gel in regeneration of full-thickness wounds was studied in nude mice. We found significantly accelerated wound closure already on day 15 in animals treated with PSG only or PSG + hPBMCs compared to untreated and hyaluronic acid-treated controls (p < 0.05). Addition of the hPBMCs to the gel resulted in marked increase of host blood vessels as well as the presence of human blood vessels. At day 25, histologically, the wounds in animals treated with PSG only or PSG + hPBMCs were completely closed compared to those of controls. Thus, the gel facilitated generation of new skin with well-arranged epidermal cells and restored bilayer structure of the epidermis and dermis. These results suggest that porcine skin ECM gel together with human cells may be a novel and promising biomaterial for medical applications especially for patients with acute and chronic skin wounds.

Acceleration of Collagen Breakdown by Extracellular Basic pH in Human Dermal Fibroblasts

BACKGROUND/AIMS

Wound healing is a complex regeneration process involving the degradation and reassembly of connective tissues and skin layers. Previous studies have shown that pH plays a significant role in both the direct and indirect regulation of cellular processes in the wound, which, in turn, affect the wound healing process. However, the effects of pH on the collagen breakdown component of wound healing have yet to be investigated. Therefore, we investigated the induction of accelerated collagen breakdown by pH imbalance in the skin.

METHODS

Na+/H+ exchanger and metalloproteinase (MMP)-1 were analyzed spectrophotometrically, and the expression of collagen type-I-alpha-1 (COL1A1) and mitogen-activated protein kinase (MAPK) was measured by Western blotting.

RESULTS

Accelerated collagen breakdown induced by extracellular basic pH via the overproduction of reactive oxygen species (ROS) and MAPK signaling was examined in skin fibroblasts and in a three-dimensional human skin equivalent system. Basic pH (>7.50) upregulated MMP-1 and downregulated COL1A1 levels via ROS generation and MAPK signaling pathways. Acidic pH (<6.04) slightly upregulated MMP-1 and slightly downregulated COL1A1 levels via ROS generation and the p38 signaling pathway.

CONCLUSION

Our results indicate that skin pH is an important effector of collagen formation in wound healing. This finding will aid in the development of new pH-targeted therapeutic strategies.

Correction of MFG-E8 Resolves Inflammation and Promotes Cutaneous Wound Healing in Diabetes

Milk fat globule epidermal growth factor-factor 8 (MFG-E8) is a peripheral glycoprotein that acts as a bridging molecule between the macrophage and apoptotic cells, thus executing a pivotal role in the scavenging of apoptotic cells from affected tissue. We have previously reported that apoptotic cell clearance activity or efferocytosis is compromised in diabetic wound macrophages. In this work, we test the hypothesis that MFG-E8 helps resolve inflammation, supports angiogenesis, and accelerates wound closure. MFG-E8(-/-) mice displayed impaired efferocytosis associated with exaggerated inflammatory response, poor angiogenesis, and wound closure. Wound macrophage-derived MFG-E8 was recognized as a critical driver of wound angiogenesis. Transplantation of MFG-E8(-/-) bone marrow to MFG-E8(+/+) mice resulted in impaired wound closure and compromised wound vascularization. In contrast, MFG-E8(-/-) mice that received wild-type bone marrow showed improved wound closure and improved wound vascularization. Hyperglycemia and exposure to advanced glycated end products inactivated MFG-E8, recognizing a key mechanism that complicates diabetic wound healing. Diabetic db/db mice suffered from impaired efferocytosis accompanied with persistent inflammation and slow wound closure. Topical recombinant MFG-E8 induced resolution of wound inflammation, improvements in angiogenesis, and acceleration of closure, upholding the potential of MFG-E8-directed therapeutics in diabetic wound care.

Paracrine Factors from Irradiated Peripheral Blood Mononuclear Cells Improve Skin Regeneration and Angiogenesis in a Porcine Burn Model

Burn wounds pose a serious threat to patients and often require surgical treatment. Skin grafting aims to achieve wound closure but requires a well-vascularized wound bed. The secretome of peripheral blood mononuclear cells (PBMCs) has been shown to improve wound healing and angiogenesis. We hypothesized that topical application of the PBMC secretome would improve the quality of regenerating skin, increase angiogenesis, and reduce scar formation after burn injury and skin grafting in a porcine model. Full-thickness burn injuries were created on the back of female pigs. Necrotic areas were excised and the wounds were covered with split-thickness mesh skin grafts. Wounds were treated repeatedly with either the secretome of cultured PBMCs (Sec(PBMC)), apoptotic PBMCs (Apo-Sec(PBMC)), or controls. The wounds treated with Apo-Sec(PBMC) had an increased epidermal thickness, higher number of rete ridges, and more advanced epidermal differentiation than controls. The samples treated with Apo-Sec(PBMC) had a two-fold increase in CD31+ cells, indicating more angiogenesis. These data suggest that the repeated application of Apo-Sec(PBMC) significantly improves epidermal thickness, angiogenesis, and skin quality in a porcine model of burn injury and skin grafting.

Upregulating Hif-1α by Hydrogel Nanofibrous Scaffolds for Rapidly Recruiting Angiogenesis Relative Cells in Diabetic Wound

Nonhealing chronic wounds on foot are one of the most dreaded complications of diabetes, and biomedical scaffolds remain an attractive option for repairing or regenerating tissues. Accelerating angiogenesis in the early stage after injury is critical to wound healing process; however, the scaffolds accelerate the angiogenesis in the beginning but with the acceleration of vessel network formation the scaffold network hinders the process. In this study, the water soluble drugs-loaded hydrogel nanofibrous scaffolds are designed for rapidly recruiting angiogenesis relative cells and promoting wound healing. The sustained release profile of desferrioxamine (DFO), which continues for about 72 h, leads to significantly increase of neovascularization. The majority of the scaffold is degraded in 14 d, leaving enough space for cell proliferation and vessel formation. The in vitro results show that the scaffolds upregulate the expression of Hif-1α and vascular endothelial growth factor, and enhance the interaction between fibroblasts and endothelial cells. The in vivo studies show a higher expression of angiogenesis related cytokines. This study demonstrates that the DFO released from hydrogel nanofibrous scaffolds of quick degradation can interfere with the required prolyl-hydroxylases cofactors by acting as Fe(2+) chelator and upregulate the expression of Hif-1α, leading to a significant increase of the neovascularization.

Evaluation of a bilayered, micropatterned hydrogel dressing for full-thickness wound healing

Nearly 12 million wounds are treated in emergency departments throughout the United States every year. The limitations of current treatments for complex, full-thickness wounds are the driving force for the development of new wound treatment devices that result in faster healing of both dermal and epidermal tissue. Here, a bilayered, biodegradable hydrogel dressing that uses microarchitecture to guide two key steps in the proliferative phase of wound healing, re-epithelialization, and revascularization, was evaluated in vitro in a cell migration assay and in vivo in a bipedicle ischemic rat wound model. Results indicate that the Sharklet™-micropatterned apical layer of the dressing increased artificial wound coverage by up to 64%, P = 0.024 in vitro. In vivo evaluation demonstrated that the bilayered dressing construction enhanced overall healing outcomes significantly compared to untreated wounds and that these outcomes were not significantly different from a leading clinically available wound dressing. Collectively, these results demonstrate high potential for this new dressing to effectively accelerate wound healing.

High-resolution harmonics ultrasound imaging for non-invasive characterization of wound healing in a pre-clinical swine model

This work represents the first study employing non-invasive high-resolution harmonic ultrasound imaging to longitudinally characterize skin wound healing. Burn wounds (day 0-42), on the dorsum of a domestic Yorkshire white pig were studied non-invasively using tandem digital planimetry, laser speckle imaging and dual mode (B and Doppler) ultrasound imaging. Wound depth, as measured by B-mode imaging, progressively increased until day 21 and decreased thereafter. Initially, blood flow at the wound edge increased up to day 14 and subsequently regressed to baseline levels by day 21, when the wound was more than 90% closed. Coinciding with regression of blood flow at the wound edge, there was an increase in blood flow in the wound bed. This was observed to regress by day 42. Such changes in wound angiogenesis were corroborated histologically. Gated Doppler imaging quantitated the pulse pressure of the primary feeder artery supplying the wound site. This pulse pressure markedly increased with a bimodal pattern following wounding connecting it to the induction of wound angiogenesis. Finally, ultrasound elastography measured tissue stiffness and visualized growth of new tissue over time. These studies have elegantly captured the physiological sequence of events during the process of wound healing, much of which is anticipated based on certain dynamics in play, to provide the framework for future studies on molecular mechanisms driving these processes. We conclude that the tandem use of non-invasive imaging technologies has the power to provide unprecedented insight into the dynamics of the healing skin tissue.

Systemic administration of hemoglobin improves ischemic wound healing

BACKGROUND

Oxygen plays multifaceted roles in wound healing, including effects on cell proliferation, collagen synthesis, angiogenesis, and bacterial killing. Oxygen deficit is a major factor in the pathogenesis of chronic wounds.

MATERIALS AND METHODS

We present a novel mechanism for oxygen delivery to ischemic wounds by systemic administration of an oxygen carrier substitute derived from bovine hemoglobin (IKOR 2084) in our ischemic rabbit ear wound model. The wound healing indexes, including epithelial gap and neo-granulation tissue area, were histologically analyzed. In situ expression of endothelial cells (CD31+) and proliferative cells (Ki-67+) were examined by immunohistochemistry analysis. The messenger RNA expression of collagen I, III, and vascular endothelial growth factor was measured by quantitative RT-PCR. Sirius Red staining was implemented for detection of collagen deposition, and terminal deoxynucleotidyl transferase dUTP nick end labeling analysis was performed to examine dermal cellular apoptosis.

RESULTS

Systemic administration of IKOR 2084 significantly improved oxygen tension of ischemic tissue. When compared with saline controls, IKOR 2084 treatment enhanced wound repair as demonstrated by a reduced epithelial gap and increased granulation tissue area. The expression of Ki-67+, CD31+, vascular endothelial growth factor and collagen was also enhanced by IKOR 2084 administration. Moreover, apoptosis analysis in the wounds showed that cell survival in the dermis was increased by systemic IKOR 2084 administration.

CONCLUSIONS

Our study suggests that systemic delivery of IKOR 2084 ameliorates hypoxic state, subsequently promotes angiogenesis, cellular proliferation, and collagen synthesis, attenuates hypoxia-induced apoptosis, and improved ischemic wound healing.

A modified collagen gel dressing promotes angiogenesis in a preclinical swine model of chronic ischemic wounds

We recently performed proteomic characterization of a modified collagen gel (MCG) dressing and reported promising effects of the gel in healing full-thickness excisional wounds. In this work, we test the translational relevance of our aforesaid findings by testing the dressing in a swine model of chronic ischemic wounds recently reported by our laboratory. Full-thickness excisional wounds were established in the center of bipedicle ischemic skin flaps on the backs of animals. Ischemia was verified by laser Doppler imaging, and MCG was applied to the test group of wounds. Seven days post wounding, macrophage recruitment to the wound was significantly higher in MCG-treated ischemic wounds. In vitro, MCG up-regulated expression of Mrc-1 (a reparative M2 macrophage marker) and induced the expression of anti-inflammatory cytokine interleukin (IL)-10 and of fibroblast growth factor-basic (β-FGF). An increased expression of CCR2, an M2 macrophage marker, was noted in the macrophages from MCG treated wounds. Furthermore, analyses of wound tissues 7 days post wounding showed up-regulation of transforming growth factor-β, vascular endothelial growth factor, von Willebrand's factor, and collagen type I expression in MCG-treated ischemic wounds. At 21 days post wounding, MCG-treated ischemic wounds displayed higher abundance of proliferating endothelial cells that formed mature vascular structures and increased blood flow to the wound. Fibroblast count was markedly higher in MCG-treated ischemic wound-edge tissue. In addition, MCG-treated wound-edge tissues displayed higher abundance of mature collagen with increased collagen type I : III deposition. Taken together, MCG helped mount a more robust inflammatory response that resolved in a timely manner, followed by an enhanced proliferative phase, angiogenic outcome, and postwound tissue remodeling. Findings of the current study warrant clinical testing of MCG in a setting of ischemic chronic wounds.

Isolation of endothelial cells and pericytes from swine corpus luteum

From an angiogenesis perspective, the ovary offers a unique opportunity to study the physiological development of blood vessels. The first purpose of this work was to set up a protocol for the isolation of pig corpus luteum endothelial cells, which were characterized by both morphologic parameters and the expression of typical molecular markers; we also verified their ability to form capillary-like structures in a 3-dimensional matrix, their response to hypoxia and their migration in the presence of vascular endothelial growth factor (VEGF). The effectiveness of our isolation protocol was confirmed by the characteristic "cobblestone shape" of isolated cells at confluence as well as their expression of all the examined endothelial markers. Our data also showed a significant cell production of VEGF and nitric oxide. Isolated endothelial cells were also responsive to hypoxia by increasing the expression and production of VEGF and decreasing that of nitric oxide. In the angiogenesis bioassay, cells displayed the ability of forming capillary-like structures and also exhibited a significant migration in the scratch test. Our data suggest that the isolation of luteal endothelial cells represents a promising tool in experiments designed to clarify the biology of the angiogenic process. Furthermore, we have demonstrated that the isolated population comprises a subset of cells with a multidifferentiative capacity toward the chondrocytic and adipocytic phenotypes. These data suggest the presence of a perivascular or adventitial cell niche in the vascular wall of the corpus luteum populated with cells showing mesenchymal stem cell-like features, as already demonstrated for the adipose tissue and endometrium.